Iet Optoelectronics最新文献

Coherent Rayleigh scattering-based distributed fibre optic sensing technology enables real-time acquisition of vibration and acoustic information along the optical fibres. However, the complexity of monitoring environments often leads to false alarms and missed detections during the process of information source identification with distributed acoustic sensing (DAS). Therefore, it becomes crucial to effectively extract meaningful signal features and perform accurate pattern recognition in the presence of external noise disturbance. The authors provide a comprehensive review of signal feature extraction and pattern recognition techniques applied in DAS technology. After introducing the fundamentals of DAS, specific applications are considered, and the following techniques have been analysed and compared: feature extraction algorithms based on wavelet decomposition, feature extraction schemes utilising other decomposition models, traditional recognition classifiers, and neural network-based recognition classifiers using deep learning. The advantages and limitations of each scheme are discussed, along with their potential applications in various scenarios. The aim is to provide insights into the latest technologies in signal processing and pattern recognition for DAS, fostering further advancements in this field.

The authors provide an example roadmap for realising the space division multiplexing (SDM)-based ecosystem. The authors investigate whether the new standard for multi-core fibre can be specified by considering a 125 μm standard cladding diameter and backward compatibility with the existing single-core single-mode fibre. The authors propose that well-planned standardisation activities need to be initiated considering mandatory technologies for realising the terrestrial SDM ecosystem in the near future.

Among the emerging photovoltaic technologies, solid-state dye-sensitised solar cells (ssDSSCs) have attracted considerable interest due to their cost-effective production, adjustable characteristics, and potential for lightweight and flexible applications. Nevertheless, achieving efficiencies comparable to established technologies, such as perovskite and silicon-based solar devices, have proven challenging. Herein, the device structure, Pt/PEDOT: PSS/N719 dye/PC₆₁BM/ITO is investigated theoretically using the solar cell capacitance simulator (SCAPS-1D). Groundbreaking advancement is introduced in ssDSSC design, achieving remarkable theoretical power conversion efficiency of 20.73%, surpassing the performance reported in traditional dye-based solar cell technologies. The model ssDSSC demonstrates an exceptional Fill factor of 86.64%, indicating efficient current collection; along with a modest short-circuit current density (J_sc) of 22.38 mA/cm² and an impressive open-circuit voltage (V_oc) of 1.0691 V, highlighting efficient light absorption and charge separation. Mott–Schottky capacitance analysis and parasitic resistances (series and shunt) have been thoroughly discussed. Despite the fact that only numerical simulation is involved, the proposed ssDSSCs structure gives insights into the fabrication of a highly efficient solar cell that can be injected into the production workflow in order to advance the photovoltaic technology of the solid-state DSSC.

Waveguide imaging is considered as one of the most important and widely used techniques in biomedical endoscopic applications. Recently, many attempts have been made to develop ever miniaturised in vivo imaging devices for minimally invasive clinical inspections. However, miniaturisation implies using a smaller optical aperture waveguide, which may introduce pixilation artefacts and pixel-to-pixel distortion to deteriorate overall imaging quality. To overcome the constraints imposed by miniaturised waveguides, the deep learning algorithms can be an effective tool to cure the imaging distortion via post-processing, which already had encouraging results in many scenes of automatic machine-learnt imaging restoration. The authors introduce the waveguide imaging transmission and the restoration algorithms, and then discuss their possible combinations. The results show that the integration of advanced waveguides and optimised algorithms can achieve unprecedented imaging restoration than before. In the future, in order to fill the need for high-quality reconstructed images, we should not only improve ability of software to optimise restoration algorithms but also correspondingly concern hardware progress in waveguides. The practical sense of it is to help researchers better master and take advantage of these combinations to make next generation high-fidelity endoscopes.

A model is presented for calculating the electric field profiles of transverse modes in fibres. Using this model, the electric field propagation of transverse modes was calculated and compared in both bent and straight Yb and Ho fibres. Our simulations revealed that the field intensities of the modes did not consistently increase or decrease by bending as expected, but rather fluctuated as the bending radii of the fibres changed from 1 to 100 cm. Additionally, it was observed that at certain bending radii, the modes of the fibres became deformed and transitioned into higher modes. Furthermore, the extent to which the modes stretched towards cladding due to bending was calculated. To provide a more comprehensive analysis of the results and investigate the effects of the physical parameters of the fibres on the bent fibre modes, simulation results were presented for two different V numbers and core radii.

A method that combines phase-sensitive optical time domain reflectometry with deep learning to construct new voting fully convolution neural networks (VoteFCNs) is proposed. Compared to the traditional convolutional network, the VoteFCN can be input with data of random size and requires less parameters so that the training speed can be improved greatly. The recognition results can be more accurate and more reliable if we use classification voting count and average recognition rate as the criteria to judge network training quality. At last, the training and identification were conducted by simulating such several disturbance events: walking, raining, climbing fence, hammering the ground optical fibre and normal outdoor environments. The results show that the average test accuracy of this method is about 93.4%.

Point-to-point (P2P) flexible transceivers are the key technical enabler to cost-effectively offer fast, dynamic, and ‘just-the-right-size’ ultra-dense P2P connectivity for various applications including remote equipment control and distributed fibre networks. However, existing flexible transceivers originally designed for hub-and-spoke traffic patterns are sub-optimal. To effectively address such technical issue, a P2P flexible transceiver incorporating a cascaded inverse fast fourier transform/fast fourier transform-based multi-channel aggregation/de-aggregation technique and analogue in-phase and quadrature (IQ) mixers is proposed and numerically evaluated in a 56Gbps@20 km intensity modulation and direct detection transmission system. The proposed P2P flexible transceivers not only support adaptive and flexible variations in both channel count and channel line rate but also offer additional physical layer network security.

The optical losses and the refractive index change of optical planar waveguides formed by MeV ion implantation were correlated with the experimental ion implantation parameters. Direct ion implantation was performed by means of carbon, silicon and copper ion beams impinging on the substrate surface at normal incidence. The ions were accelerated at energies ranging from 3 to 12 MeV with fluences varying from 1 × 10¹² to 2 × 10¹⁶ ion/cm², according to the type of implanted ion. The modification of the substrate refractive index due to the ion irradiation-induced damage was evaluated using the prism coupler method, and the refractive index profiles were determined by means of a reconstruction method using a multilayer structure approximation. The guiding properties of the waveguides were analysed using the fibre-coupling technique to determine both the optical transmission and transversal modes at 635 nm. The main practical relevance of our research is the obtention of high-quality waveguides at low current density MeV ion implantation (≤80 nA/cm²) without post-implantation annealing.

An enhanced transmission is presented in a multiple-input-multiple-output (MIMO) dense-wavelength division multiplexed (DWDM) free-space-optical (FSO) communication link using diversity coding techniques under the effect of turbulent weather phenomenon. The findings show good performance with an (8 channels × 2.5 Gbps data rate/channel) 20 Gbps 1500 m transmission distance. The bit-error-rate (BER), outage probability (OP), and signal-to-noise ratio (SNR) of the diversity combining techniques using maximum-ratio combining (MRC), selection combining (SC), and equal-gain combining (EGC) technique are evaluated in this work. The obtained results illustrate that Alamouti, space-time coding (STC), space-time block coding (STBC), space-time trellis code (STTC), orthogonal STBC (O-STBC), and quasi-orthogonal STBC (QO-STBC) on the minimum mean-square-error, and MRC are worth implementing on the DWDM-FSO wireless communication systems. The mitigation of atmospheric turbulence is achieved using MIMO diversity combining techniques coding. The simulation results for diversity coding techniques using QO-STBC/STTC and SC/MRC in the MIMO-DWDM FSO communication system can improve BER performance, OP, and SNR. The MRC exhibits the lowest OP and BER when compared with the SC and EGC. The numerical results demonstrate that the FSO communication link using DWDM QO-STBC/STTC improves the power penalty at both BER values under varying atmospheric turbulence conditions for ST, MT, and WT, in comparison to FSO systems without DWDM QO-STBC/STTC diversity coding techniques.

The authors analyse the influence of reference sphere on the test accuracy of Ritchey–Common method during testing of flat mirror surface. A simulation model is established to simulate the influence of different radii of curvature of reference sphere on system wavefront. Then, the difference between the flat mirror surface result with reference sphere surface error to the actual flat mirror surface is examined by this model. The test accuracy of flat mirror result can be effectively improved by eliminating the influence of the surface error of reference sphere. When the surface accuracy of the reference sphere is better than 0.01 λ, the influence on RMS test accuracy is within 0.01 λ. R–C test path is built to test a 100 mm-diameter flat mirror surface, and its results are compared with those of the flat mirror surface without surface error of reference sphere and with the test result of the interferometer. When the surface accuracy of the actual used area of reference sphere is better than 0.01 λ, the effect on flat mirror RMS accuracy is within 0.01 λ. The RMS test accuracy can reach 0.01 λ, when the surface error of reference sphere is retained. The experiment verifies the correctness of the simulation results and guarantees the improvement in the test accuracy of R–C method.